New details have emerged about alleged "health attacks" on US diplomats in Cuba which indicate at least some of the incidents were confined to specific rooms or even parts of rooms with laser-like specificity.
The Associated Press learned that in one case, an American diplomat was jolted from his bed in a Havana hotel by a blaring, grinding noise.
It went silent when he moved a few feet away, and it returned when he stepped back into bed.
Soon he began suffering from hearing loss and speech problems, symptoms both similar and different from others among at least 21 US victims.
The incidents, which the American called "health attacks", have been baffling US officials who say the facts and the physics do not add up.
"None of this has a reasonable explanation," said Fulton Armstrong, a former CIA official who served in Havana long before America re-opened an embassy there.
"It's just mystery after mystery after mystery."
Suspicion initially focused on a sonic weapon and on the Cubans.
Yet the diagnosis of mild brain injury, considered unlikely to result from sound, has confounded the FBI, the State Department and US intelligence agencies involved in the investigation.
Some victims now have problems concentrating or recalling specific words, several officials said, the latest signs of more serious damage than the US government initially realised.
The United States first acknowledged the attacks in August - nine months after symptoms were first reported.
The Trump administration still has not identified a culprit or a device to explain the attacks, according to interviews with more than a dozen current and former US officials, Cuban officials and others briefed on the investigation.
In fact, almost nothing about what happened in Havana is clear.
Investigators have tested several theories about an intentional attack - by Cuba's government, a rogue faction of its security forces, a third country like Russia, or some combination thereof.
Yet they have left open the possibility an advanced espionage operation went horribly awry, or that some other, less nefarious explanation is to blame.
Aside from their homes, officials said Americans were attacked in at least one hotel, a fact not previously disclosed.
An incident occurred on an upper floor of the recently renovated Hotel Capri, a 60-year-old concrete tower steps from the Malecon, Havana's famous waterside promenade.
The cases vary deeply: different symptoms, different recollections of what happened - making the puzzle difficult to crack.
In several episodes recounted by US officials, victims knew it was happening in real time, and there were strong indications of a sonic attack.
Some felt vibrations, and heard sounds - loud ringing or a high-pitch chirping similar to crickets or cicadas. Others heard a grinding noise.
Some victims awoke with ringing in their ears and fumbled for their alarm clocks, only to discover the ringing stopped when they moved away from their beds.
The scope keeps widening. On Tuesday, the State Department disclosed that doctors had confirmed another two cases, bringing the total American victims to 21.
Some have mild traumatic brain injury, known as a concussion, and others permanent hearing loss.
Even the potential motive is unclear. Investigators are at a loss to explain why Canadians were harmed, too, including some who reported nosebleeds.
Fewer than 10 Canadian diplomatic households in Cuba were affected, a Canadian official said.
Unlike the US, Canada has maintained warm ties to Cuba for decades.
Sound and health experts are equally baffled. Targeted, localised beams of sound are possible, but the laws of acoustics suggest such a device would probably be large and not easily concealed.
Officials said it is unclear whether the device's effects were localised by design or due to some other technical factor.
And no single sonic gadget seems to explain such an odd, inconsistent array of physical responses.
"Brain damage and concussions, it's not possible," said Joseph Pompei, a former MIT researcher and psycho-acoustics expert.
"Somebody would have to submerge their head into a pool lined with very powerful ultrasound transducers."
Other symptoms have included brain swelling, dizziness, nausea, severe headaches, balance problems and tinnitus, or prolonged ringing in the ears.
Many victims have shown improvement since leaving Cuba and some suffered only minor or temporary symptoms.
Cuba's government declined to answer specific questions about the incidents, pointing to a previous Foreign Affairs Ministry statement denying any involvement, vowing full co-operation and saying it was treating the situation "with utmost importance".
"Cuba has never, nor would it ever, allow that the Cuban territory be used for any action against accredited diplomatic agents or their families, without exception," the Cuban statement said.